title: Hospital outpatients are satisfactory for case-control studies on cancer and diet in China: a comparison of population versus hospital controls.
abstract: BACKGROUND
  To investigate the internal validity of a food-frequency questionnaire (FFQ) developed for use in Chinese women and to compare habitual dietary intakes between population and hospital controls measured by the FFQ.
  
  
  METHODS
  A quantitative FFQ and a short food habit questionnaire (SFHQ) were developed and adapted for cancer and nutritional studies. Habitual dietary intakes were assessed in 814 Chinese women aged 18-81 years (407 outpatients and 407 population controls) by face-to-face interview using the FFQ in Shenyang, Northeast China in 2009-2010. The Goldberg formula (ratio of energy intake to basal metabolic rate, EI/BMR) was used to assess the validity of the FFQ. Correlation analyses compared the SFHQ variables with those of the quantitative FFQ. Differences in dietary intakes between hospital and population controls were investigated. Odds ratios (ORs) and 95% confidence intervals (CIs) were obtained using conditional logistic regression analyses.
  
  
  RESULTS
  The partial correlation coefficients were moderate to high (0.42 to 0.80; all p<0.05) for preserved food intake, fat consumption and tea drinking variables between the SFHQ and the FFQ. The average EI/BMR was 1.93 with 88.5% of subjects exceeding the Goldberg cut-off value of 1.35. Hospital controls were comparable to population controls in consumption of 17 measured food groups and mean daily intakes of energy and selected nutrients.
  
  
  CONCLUSIONS
  The FFQ had reasonable validity to measure habitual dietary intakes of Chinese women. Hospital outpatients provide a satisfactory control group for food consumption and intakes of energy and nutrients measured by the FFQ in a Chinese hospital setting.
authors.affiliation: School of Population Health, Faculty of Medicine, Dentistry and Health Sciences, University of Western Australia , Perth, Australia. min.zhang@uwa.edu.au
authors.forename: Lin
authors.initials: L
authors.lastname: Li
authors.forename: Min
authors.initials: M
authors.lastname: Zhang
authors.forename: C D'Arcy J
authors.initials: CD
authors.lastname: Holman
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D002681:China; D004032:Diet; D015930:Diet Records; D004041:Dietary Fats; D005247:Feeding Behavior; D005260:Female; D057141:Food, Preserved; D006801:Humans; D007297:Inpatients; D008875:Middle Aged; D009369:Neoplasms; D010045:Outpatients; D015203:Reproducibility of Results; D015983:Selection Bias; D011795:Surveys and Questionnaires; D013662:Tea; D055815:Young Adult
chemical_list: D004041:Dietary Fats; D013662:Tea